This invention relates to a protective relay for protecting a portion of a high voltage transmission line, and more particularly, to a characteristic timer having one or more selectable activation times for a protective relay.
Characteristic timers are frequently employed in protective relays for determining the activation time of the protective relay. One such characteristic timer is described in my U.S. Pat. application Ser. No. 369,440, filed Apr. 19, 1982, assigned to the same assignee of the present invention and herein incorporated by reference.
U.S. Pat. application Ser. No. 369,440, referred to above, describes a characteristic timer having digital logic that is responsive to an external device for, among other things, (1) easily selecting a phase angle representative of the activation time of the protective relay, and (2) reducing the resetting time of the protective relay so as to reduce the resetting time of the protective relay system. Although my hereinbefore given U.S. Pat. application functions well for its desired objectives it is considered desirable that a characteristic timer be provided with further advantages, such as, (1) means for easily selecting at the same time one or more phase angles each representative of a desired activation time, (2) a selectable "integrating" or "non-integrating" function, (3) means for clearing or resetting the digital logic in response to an external fault condition, and (4) the similar advantage of my hereinbefore given U.S. Pat. application in that the protective relay has means for reducing its resetting time. The term "integrating" is meant to represent that the characteristic timer monitors an applied signal for more than one cycle of the applied signal and integrates the result. Conversely, "non-integrating" is meant to represent that the monitoring and the result of the characteristic timer are dependent on one-cycle of the applied signal.
Accordingly, objects of the present invention are to provide (1) means for easily selecting at the same time one or more phase angles each representative of a desired activation time of the characteristic timer, (2) an integrating or non-integrating type of operation for the characteristic timer selectable by an external input, (3) means for clearing or resetting the digital logic of the characteristic time in response to an external fault condition, and (4) a means for reducing the reset time of the protective relay.
These and other objects of the present invention will become apparent to those skilled in the art upon consideration of the following description of one form of the invention.